Facile Synthesis of Ordered Mesoporous Alumina and Alumina-Supported Metal Oxides with Tailored Adsorption and Framework Properties

Abstract

The evaporation-induced self-assembly (EISA) in ethanolic solution of a triblock copolymer (Pluronic P123) is explored for the synthesis of ordered mesoporous alumina (MA) and MA-supported metal oxides, using aluminum isopropoxide, aluminum chloride, and aluminum nitrate nonahydrate as aluminum precursors, and nickel, magnesium, iron, chromium, copper, cerium, lanthanum, yttrium, calcium, tin chlorides, or nitrates as metal precursors. The as-synthesized mesoporous oxides were characterized by a variety of techniques, such as thermogravimetry, Fourier transform infrared spectroscopy, nitrogen adsorption, small- and wide-angle X-ray diffraction, high-resolution transmission electron microscopy, energy-dispersive X-ray spectrometry, elemental mapping, and CO 2 and NH 3 temperature-programmed desorption. It is shown that the EISA strategy in the presence of polymeric template not only is well-suited for the synthesis of ordered MAs and MA-supported metal oxides with tailored adsorption and framework properties, but also ensures a homogeneous distribution of metal species within inorganic framework with the aluminum/metal atomic ratio close to this used in the synthesis mixture. The aluminum and other metal precursors used in EISA have a significant impact on the pore structure, surface area, and basic and acidic properties of the resulting mixed oxides. For instance, the use of inexpensive aluminum nitrate nonahydrate in the synthesis leads to the significantly enlarged mesopores (ranging from ∼7 nm to 16 nm), improved ordering of the oxides, and enhanced adsorption affinity toward CO 2, while the aluminum chloride precursor affords MA-supported metal oxides with a bimodal pore size distribution, with peaks located in the ranges of 2−4 nm and 5−9 nm, respectively. It is also shown that the use of inexpensive aluminum and metal salts as precursors instead of aluminum alkoxides affords MA-supported metal oxides with tailorable properties, in terms of the surface area, porosity, and surface basicity and acidity, which determine the performance of these materials in various applications, including adsorption and catalysis.